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首页> 外文期刊>Hadronic Journal >ORIGIN OF THE TORQUOSELECTIVITY OBSERVED IN THE THERMAL RING-OPENING OF CYCLOBUTENES BASED ON THE CPLEX-ISOELECTRONIC THEORY AND EXPANDED ROBINSON ELECTRONIC THEORY
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ORIGIN OF THE TORQUOSELECTIVITY OBSERVED IN THE THERMAL RING-OPENING OF CYCLOBUTENES BASED ON THE CPLEX-ISOELECTRONIC THEORY AND EXPANDED ROBINSON ELECTRONIC THEORY

机译：基于CP-等电子理论和扩展的罗宾逊电子理论的环戊二烯热开环中观察到的选择性的起源

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摘要

The Cplex-isoelectronic theory provides rationales for the torquoselectivities in the ring-opening of cyclobutenes. Electron donors at C3 rotate outwards due to the carbanion-like (σ~-) C4 rotating away from the 3-electron donor in the 1' process (first stage) of the electronic mechanism. C4 becomes σ~- due to heterolytic fission of the C3-C4 single bond. Rotation of C4 away from the 3-electron donor also maximizes the assistance (SEADEF) provided by the 3-electron donor in the heterolytic fission of the C3-C4 bond. Electron withdrawing groups at C3 are predicted not to exhibit a torquoelectronic effect as the carbanion-like (σ~-) C3 rotates away and past a H substituent at C4 during clockwise and anticlockwise rotation. Thus stereoselectivity is determined by conventional steric and electronic effects. C-3 becomes σ~- and C-4 becomes σ~+ due to heterolytic fission of the C3-C4 single bond. Inward rotation of the 3-formyl group is proposed to be due to the stabilization of the carbocation-like (σ~+) C4 by electron donation from the lone pair of the trigonal C=O group. The lone pair must be close to C-4 at the early stages of the reaction. Si, Sn, Ge and B substituents at C3 rotate inwards due to their stabilization of the carbocation-like (σ~+) C4 via the β-effect. The 3-halides are considered as electron withdrawing groups and thus are predicted not to exhibit a torquoelectronic effect. The outward rotation of the Me group, relative to the ethyl and isopropyl group, in 3-alkyl-3-methylcyclobutenes is proposed to be due to a greater degree of rotation of the carbanion-like (σ~-) C-4 away from the 3-methyl group in the 1' process because of the greater σ~- on the C of the methyl group relative to the α-C of the ethyl and isopropyl groups. Inward rotation of an electron donor in disrotatory ring openings is predicted and outward or inward rotation of Si depending on the substrate. This prediction is best tested in large puckered rings. The torquoselectivity patterns observed for conrotatory systems is predicted to change to the torquoselectivity patterns observed for disrotatory systems on replacing all the double bonds with strained ring systems (e.g. norbornene). These rationales and predictions are compared to those produced by quantum chemistry and many differences are found.
机译：Cplex-等电子理论为环丁烯开环中的选择性提供了理论依据。在电子机构的1'过程（第一阶段）中，由于碳负离子状（σ〜-）C4旋转远离3电子给体，因此C3处的电子给体向外旋转。由于C3-C4单键的杂合裂变，C4变为σ-。 C 4远离3电子给体的旋转还使3电子给体在C 3-C 4键的异裂变中提供的辅助作用（SEADEF）最大化。预测在顺时针和逆时针旋转过程中，碳原子状（σ〜-）C3旋转离开并经过C4处的H取代基时，C3处的吸电子基团不会表现出扭转电子效应。因此，立体选择性由常规的空间效应和电子效应决定。由于C3-C4单键的杂合裂变，C-3变为σ〜-，而C-4变为σ〜+。提出3-甲酰基的向内旋转是由于通过来自三角形C ＝ O基团的孤对的给电子而使碳正离子状（σ〜+）C 4稳定。在反应的早期，孤对必须接近C-4。 C3处的Si，Sn，Ge和B取代基由于通过β效应使碳正离子状（σ〜+）C4稳定而向内旋转。 3-卤化物被认为是吸电子基团，因此预计不会表现出扭转电子效应。有人提出，在3-烷基-3-甲基环丁烯中，Me基相对于乙基和异丙基的向外旋转是由于碳负离子状（σ〜-）C-4的旋转度更大因为在甲基的碳原子上相对于乙基和异丙基的α-C较大的σ--，所以在1'过程中形成了3-甲基。可以预测在旋转环开口中电子给体的向内旋转，并且取决于衬底，Si的向外或向内旋转。最好在大皱纹戒指中测试此预测。当用应变环系统（例如降冰片烯）代替所有双键时，预计在旋转系统中观察到的扭转选择性模式将改变为在旋转系统中观察到的扭转选择性模式。将这些原理和预测与量子化学产生的原理和预测进行了比较，发现了许多差异。

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    《Hadronic Journal》 |2009年第4期|341-394|共54页
  • 作者

    Martin O. Cloonan;

  • 作者单位

    Chemistry, School of Science, Galway-Mayo Institute of Technology Dublin Road, Galway, Republic of Ireland;

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